pT7-FLuc-A50, pT7-PV-FLuc-A50, and pT7-EMCV-FLuc-A50 were linearized with NotI and transcribed with HiScribe T7 High yield RNA Synthesis Kit according to manufacturer's instructions (New England Biolabs). For NanoLuc reporters with differing 5′ UTR lengths, pNL1.1 (Promega) was used as a PCR template. Forward primers contained a T7 promoter for transcription and were positioned to generate the indicated 5′ UTR length. Reverse primer added a synthetic poly(A) tail. RNAs was transcribed with HiScribe T7 High yield RNA Synthesis Kit according to manufacturer's instructions (New England Biolabs). In vitro translation assays were performed as previously described (4 (link)).